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Forum Topic - acetal alternate
acetal alternate
By plasticsgerry, Aug 25, 2008
I'm trying to make an acetal valve seal. Cone shaped part with a hole through both sides. Parts look and measure fine but fail pressure testing. I h
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By Brent, Mar 31, 2008 at 12:34
Bruce, Have you tried an Acetal Copolymer, such as CELCON M-90? brent
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By Bruce, Mar 31, 2008 at 13:01
Just came back from customers place. It turns out the parts are cold flowing due to high pressure. You would think that they might crack etc but it is just deformed enough to leak and then they take the pressure off. So I think I need a higher tensile strength and higher flex modulus. I was looking at Delrin 510GR, shrink is a bit less but tensile is up at 14,500 and flex is 624K. Much higher than the 500AF. Anyone ever run this? Or other suggestions?
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By Brent, Apr 07, 2008 at 17:21.
Run it in a pawl that goes on a zipper assembly. Don't mold it with a cold mold. I think we are around 185°F. I'll look it up if you want me to. The parts are very small. brent
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By Brent, Apr 07, 2008 at 17:24.
Bruce, Yes we do, in small parts that go into a zipper assembly. Don't run a cold mold is my advice. I think we run about 185°F Let me know if you want me to look it up. brent a href="http://www.matrixtooling.com">Matrix Tooling, Inc. | Matrix Plastic Products
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By Brent, Apr 07, 2008 at 17:45.
Bruce, We run 510 GR in small pawls that go into zipper assemblies. I wouldn't run a cold mold. We run about 185°F. Let me know if you want me to look it uo. brent
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By Bruce, Apr 08, 2008 at 20:54.
Brent I was saying the parts were "cold flowing" ie distorting when under pressure. I ran the mold at 180, I think. I have a few grades of Acetal coming with 5, 10 and 20% glass. I'm thinking the 5% will do it. I will post results.
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By rickbatey, Apr 09, 2008 at 7:54.
Would a higher mold temp change the crystallinity, and therefore affect the creep? Perhaps a much hotter tool with tons of pack could correct/diminish the problem....Rick.
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By Lisa_C, Apr 11, 2008 at 13:11.
We have worked with DuPont in the past, as we run alot of their acetals and we had a part shrinking abnormally. Our mold was too cold, they said. Hotter mold will make for a more crystalline part and control shrinkage better, according to them.
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By Bruce, Apr 22, 2008 at 21:05.
Well I ran samples of a LNP 20% glass filled Acetal, as I suspected they work! Finally! Of course the shrink is off a bit but it looks like it works. Also ran LNP 20% glass/15%PTFE and those parts were like "marshmallows" to quote the customer. Today I ran more samples of a 10% glass filled Acetal. If these pass, then I will have more comfort with the 20% glass. These do seem to be a bit smaller. By the way, I have had the mold up to 190F for the above 3 runs. When I do more, I will try up to 210F and see if I can measure any more shrinkage.
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By plasticsgerry, Apr 23, 2008 at 13:19.
I once had to run a non-filled acetal on a mold designed for 20% glass filled. Techs spent weeks trying to run the mold colder and colder and couldn't reduce the shrink. We ran the mold at 210 degrees F, and the increase in crystallization reduced the shrink and put the dimensionals right at nominal. Sometimes hotter is bigger.
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